Dopamine acts as a light-adaptive signal in the retina, where it - controls a number of different reorganizational or plastic changes which enable the retina to respond better under conditions of increased ambient illumination. The overall goal of the proposed research is to better understand the way in which light controls the release of dopamine in the retina and the effects of dopamine on the ability of different types of neurons in the retina to detect different types of light stimuli. Specific aims include determination of the type of photoreceptor which mediates light-evoked dopamine release, how dopamine release is modulated by the activity of other neurons, how the known actions of dopamine on lateral interactions in the outer retina affect the receptive field organization of more central retinal neurons, and whether dopamine also modulates lateral interactions in the inner retina. These experiments will be done using intracellular recordings of the electrical responses of individual neurons in the intact, living retina, using the eyecup preparation from an amphibian, the mudpuppy (Necturus maculosus). The retinas of this and closely related animals have been extensively studied and much is already known about their functional organization. The proposed studies may provide information relevant to the understanding of information processing in the human retina since all vertebrate retinas have a similar basic organization. In the proposed experiments, the effects of different wavelengths and patterns of light stimuli and of neurotransmitter agonists and antagonists suspected to be involved in modulation of dopamine release will be studied. Changes in dopamine release will be indicated by the changes in responses of horizontal cells to certain light stimuli; this has proven to be a reliable and very sensitive assay for changes in dopamine release in the retina. The effects of dopamine on lateral interactions in the inner retina will be studied using intracellular recording from ganglion cells.